The operation of an internal combustion engine is affected by a number of factors not the least of which is the sulfur content in the fuel supply. Typical internal combustion engine fuels such as gasoline and diesel fuel contain relatively high levels of sulfur, normally in the form of organic sulfur compounds. The specification for diesel fuel is about 500 parts per million (ppm) although the average is significantly below this level. The US average for regular gasoline is about 350 ppm. Current efforts to reduce internal combustion engine fuel sulfur levels, such as the present California Phase II specification, call for sulfur content limits in gasoline of less than about 40 ppm. The benefit of lowering sulfur content in engine fuel is a reduction in sulfur pollution levels from automobiles as well as reducing the effects of engine component corrosion and the negative effects of sulfur on the engine catalytic converters.
Sulfur oxide emissions from the automobile's internal combustion engine contributes to acid rain. In diesel engines, high sulfur levels result in increased particulate levels in the exhaust. High sulfur levels also contribute to more rapid corrosion of engine materials, and to a lowering of catalytic converter effectiveness, which means more nitrogen oxide formation, and a lower activity level for the conversion of carbon monoxide and unburned hydrocarbons.
While the California phase II specification deals with sulfur levels in the original fuel source, other sulfur clean up methods proposed to date for diesel and gasoline internal combustion engines are focused on cleaning up the exhaust after the combustion process. While these post-combustion clean up approaches can be made to work, it is far more desirable to reduce or remove the sulfur before the combustion cycle. Sulfur clean up processes for liquid fuels such as those described in an article published in connection with the 21st Power Sources Conference proceedings of May 16-18, 1967, pages 21-26, entitled "Sulfur Removal for Hydrocarbon Air Systems" require complex equipment which is not easily incorporated in a vehicle.
It would be highly desirable therefore, from an environmental, cost and equipment durability stand point to be able to power a diesel or gasoline fueled internal combustion engine by means of a desulfurized fuel, i.e., a fuel containing less than about 0.05 ppm sulfur.